You gotta go with track record sometimes, and Dallas Keuchel's indicates he's gonna be fine.
Last year, the Houston Astros left-hander had a 2.90 ERA. This year, it's 4.22. On the surface, that seems like a big regression. However, his FIP in 2017 was 3.79 and this year it's 3.92. Not that big a gap. His strikeout rate has dipped (21.4% to 18.1%) and opponents have increased their batting average against him (.217 to .263).
However, he's allowing a .301 BABIP and isn't getting as many ground balls as he did last year -- 54.2%, down from 66.8%.
With a pitcher like Keuchel, you should tend to lean on their track records. And while he's not an ace, Keuchel plays for what may be the best team in the American League and should bank a few more wins in the second half of the season.